4.2.1 Description: Project Summary and Relevance Tuberculosis still remains the number one cause of human mortality caused by infection with a bacterial pathogen. Estimates of mortality range from 1.4-2.0 million deaths globally per year. Current treatment paradigms, developed for drug sensitive strains of Mycobacterium tuberculosis, are being severely threatened by the emergence of multi- and extensively-drug-resistant strains. We have identified a cAMP-dependent protein acetyltransferase and sirtuin-like deacetylase in M. tuberculosis and have identified a small number of protein substrates for the protein acetyltransferase. These enzymes, when acetylated, lose their enzymatic activity, and when deacetylated, are again active. This reversible modification is likely to be important in the transition from rapid growth to a dormant, non-replicating phase. We will in Aim 1, continue our efforts to identify the substrate cohort for the protein acetyltransferase and identify growt conditions in which knock-out strains of the protein acetyltransferase or sirtuin are affected. Wit the development of strains of M. tuberculosis that can be grown in BSL2 laboratories, we propose in Aim 2 to identify the small molecule substrates of the 20 GNAT's in M. tuberculosis. We have developed reagents for this purpose, and will continue studies initiated in the prior period of support. In Aim 3, we wish to examine the host proteins that are substrates for the M. tuberculosis EIS protein (EIS = enhanced intracellular survival), an acetyltransferase implicated in modulating the host response to bacterial infection and macrophage ingestion. Together these aims will provide a detailed description of the acetyltransferase enzymes, and their substrates, in an organism whose metabolism is poorly understood.